1. Field of the Invention
The present invention relates to a digital camera, and more particularly, to a CCD camera using a plurality of CCDs (Charge Coupled Devices) and a method for controlling the same.
2. Description of the Related Art
As generally known in the art, a CCD camera is an apparatus which is designed to convert optical brightness into electrical amplitude signals using a plurality of CCDs, and then reproduce the image of a subject using the electric signals without time restriction. Such CCD cameras have been developed in close relation with televisions, and can operate in a frame output mode and a field output mode according to the data output methods of the CCD, similar to the scan mode of televisions.
In the frame output mode, as shown in FIG. 1, signal charges of the odd numbered pixels in the vertical direction of all the pixels (photodiodes PD) are first read in the photosensitive unit (see (a) of FIG. 1), and signal charges of the even numbered pixels are read at the next field (see (b) of FIG. 1). In this case, the frame output mode is also called a frame accumulation mode, since the duration for which signals of all pixels are accumulated corresponds to a two field period, which is referred to as “one frame period”. Similarly, since it takes one frame period in reading all pixels, it is called a frame output mode.
In the frame output mode as discussed above, each pixel is independently read, so that resolution in the vertical direction is good. However, because the frame output mode requires a time of 1/30 second in order to accumulate all pixels, a so-called frame-after-image is generated. That is, when a subject moves or a camera pan is performed, the afterimage left from the previous field image is generated, which thus may reduce image quality.
In the field output mode as shown in FIG. 2, when data are read from the CCDs, added signal charges, each of which is made by adding signal charges of each odd numbered pixel and each corresponding even numbered pixel according to the vertical direction in the odd field, are read first (see (a) of FIG. 2). Subsequently, in the even field, signal charges of even numbered and odd numbered pixels are read in the changed combination (see (b) of FIG. 2). That is, signal charges of all pixels are read with only one field. Also, the storage duration for signals of all pixels is one field period, and thereby it is called a field accumulation mode or a field output mode.
A CCD camera using the field output mode comprises a frame using data of any one field of even/odd fields read by an addition operation. That is, one frame is formed by copying an original field read by the addition process, and then by overlapping the original field and the copied field so that their horizontal lines correspond. Then, the data of the other field, which is not copied, is used to determine luminance and color image for the copied field.
In the CCD camera using the field output mode as discussed above, although a still image is read by adding adjacent pixels, the read data are only half of the entire data for the original image. Hence, image quality is reduced.
Also, if a CCD camera including the field output mode is configured to embody a still image with both of the read fields, it has a higher resolution than the camera using the method to copy one field as described above. However, a blur is generated when a moving subject is photographed. That is, while the odd/even fields are read, the image of the next field moves farther to the moving direction due to light being incident continuously. Thus, when the prior and next fields are combined with each other, an enlarged image may be shown as compared to the original image.